The present invention relates to a structure and method for leading out conductor layers from a semiconductor device and, further, to a semiconductor module using such a semiconductor device. In particular, the present invention is usefully applicable to a power amplifier using heterojunction bipolar transistors. The present invention is also useful in achieving a high conversion efficiency power amplifier.
With the rapidly growing demand for mobile communication equipment, active research and development efforts are recently directed to power amplifiers for use in communication equipment. To meet the needs for smaller communication tools, MMICs (Monolithic Microwave Integrated Circuits) are used in power amplifier modules. An MMIC contains semiconductor chips together with passive elements. Transistors popular in these MMICs are heterojunction bipolar transistors (HBTS) due to superiority in power density and miniaturization. Especially in a miniaturization-oriented power amplifier module, a MMIC is mounted face down to a ceramic substrate by using metal bumps. A representative example of this technique is found, for example, in “Solid State Electronics” (Vol. 38, No. 9 (1995), pp. 1653–1656). Note that in this specification, monolithic microwave integrated circuits and heterojunction bipolar transistors are abbreviated as MMICs and HBTs respectively.
FIG. 9 shows a typical prior art example of this technique. FIG. 9 is a cross-sectional view of a power amplifier module. In the conventionally typical manufacturing method, a MMIC 100 is mounted face down to a module plate. The module plate shown as an example in FIG. 9 is composed of three substrates 121, 120 and 122. On the substrate 120, an emitter wiring pad 101, base wiring pad 102 and collector wiring pad 103 are arranged. For packages, low-temperature sintered glass ceramics plates with a dielectric constant of 8 have usually been used. The substrate 121 has an opening where the MMIC 100 is accommodated. Reference numeral 104 denotes a passive element fabricated as a chip part, 105 is a transmission line, 106 is a metal bump, 107 is a base input, 108 is a collector input, 109 and 110 are each a ground plane, 111 is a thermal via, 112 is a transmission line and 113 is a metal cap.
Since face down mounting is employed in FIG. 9, variations occur in the heights of metal bumps 106. This results in nonuniformity of the distance between the surface of the MMIC 100 and the surface of the module substrate 120 as indicated by d2 and d3 in FIG. 9. Accordingly, the drawback to this method is that due to variations in the capacitance parasitic to the MMIC 100, the power amplifier involves a variability of high frequency characteristics.